Method for receiving and transmitting data blocks

ABSTRACT

The present invention provides a scalable and reliable feedback suppression method for receiving and transmitting data block. The method comprises receiving at least one initial data packet of the data block which is sent by the transmitter to the multicast group of receivers; and sending at least one NAK packet indicating packet loss to the transmitter by at least one receiver of the multicast group, wherein the at least one NAK packet is sent in a single uplink time slot dedicated to said multicast group of receivers, and wherein the NAK packet is identical for all receivers of said multicast group.

This application claims the benefit, under 35 U.S.C. §365 ofInternational Application PCT/EP2009/061048, filed Aug. 27, 2009, whichwas published in accordance with PCT Article 21(2) on Apr. 15, 2010 inEnglish and which claims the benefit of European patent application No.08305642.4, filed Oct. 6, 2008.

FIELD OF THE INVENTION

The present invention relates in general to communication network, andmore particularly to a method for receiving and transmitting data blocksin the communication network.

BACKGROUND OF THE INVENTION

The multicast and broadcast service (MBS) is a promising technology tosimultaneously transmit the same data content to a plurality of clientdevices. For example, in a wireless communication system, the wirelessterminal devices are often designed and configured to receive video,audio, and multimedia content simultaneously. Therefore, the transmitterof the wireless base station will multicast or broadcast the video,audio and multimedia content to these wireless terminal devices so thateach of the devices receives and presents the video and/or audio contentto its user.

In addition, data packet loss or error can be unavoidable andunpredictable in the communication network, especially in a wirelesscommunication network. In order to improve the quality of the receivedcontents, a loss recovery technology such as Forward Error Correction(FEC) and Automatic Repeat reQuest (ARQ) can be deployed in abi-directional communication network. The receivers are required to sendback an acknowledgement reporting whether data packets have beensuccessfully received or not. The transmitter monitors theacknowledgement (ACK), representing packets that are properly received,or negative-acknowledgment (NAK), indicating packet loss has happened.Upon reception of the feedback, the transmitter can determine whether tosend out additional parity packets or re-transmit packets.

To limit the number of feedback packets from all receivers in themulticasting system, NAK instead of ACK is used to feed back to thesender because of its lighter overhead requirement. However, for amulticast or broadcast service, the transmitter may send the same datapackets to dozens or hundreds of receivers and since the report of NAKpackets is also not predictable, data congestion can still occur in areverse uplink channel.

US2008/0031179 discloses a method to assign a feedback time slot to allreceivers with a predetermined number of packet losses in time divisionmultiplexing accessing mode. For example, receivers having experiencedone packet loss will send feedback in the first time slot, receiverssending feedback in the second time slot will have experienced twopackets losses. The required feedback bandwidth depends on the number ofpacket losses. The drawback of this method is that the transmittershould allocate an estimated number of time-slots (equal to the maximumnumber of packet losses) for the feedback transmission.

Therefore, an improved method for receiving and transmitting datacontents is needed.

SUMMARY OF THE INVENTION

The invention concerns a method for receiving a data block from atransmitter, used in a receiver part of a multicast group of receiversin a communication network, including: receiving at least one initialdata packet of the data block which is sent by the transmitter to saidmulticast group; and sending at least one NAK packet to the transmitterby said receiver if existing packet loss, wherein the at least one NAKpacket is sent in a single uplink time slot dedicated to said multicastgroup of receivers, and wherein the NAK packet is identical for allreceivers of said multicast group; further receiving at least oneadditional packet of the data block, which is sent by the transmitterbased on NAK packet from at least one receiver of said multicast group.

The invention also concerns receiver for implementing the method forreceiving a data block as mentioned above. The receiver includes meansfor receiving at least one initial data packet of the data block whichis sent by the transmitter to said multicast group; and means forsending at least one NAK packet indicating packet loss to thetransmitter by said receiver, wherein the at least one NAK packet issent in a single uplink time slot dedicated to said multicast group ofreceivers, and wherein the NAK packet is identical for all receivers ofsaid multicast group.

The invention also concerns a method for sending a data block to amulticast group of receivers, used in a transmitter of a communicationnetwork, including: sending at least one data packet of the data block;and sending at least one recovery data packet for the data block, whenat least one NAK packet is received in a single uplink time slot fromthe multicast group of receivers, wherein the NAK messages sent by theplurality of receivers are identical.

The invention also concerns a transmitter for implementing the methodfor transmitting a data block as mentioned above. The transmitterincludes means for sending at least one data packet of the data block;and means sending at least one recovery data packet for the data block,when at least one NAK packet is received in a single uplink time slotfrom the multicast group of receivers, wherein the NAK messages sent bythe multicast group of receivers are identical.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects, features and advantages of the presentinvention will become apparent from the following description inconnection with the accompanying drawings, among which:

FIG. 1 is a schematic diagram showing a wireless network implementingTime Division Multiplex (TDM) scheme used to explain an embodiment ofthe invention;

FIG. 2 is a diagram showing a TDM allocation scheme according to theembodiment of the invention;

FIG. 3 is a diagram showing a NAK message format according to theembodiment of the invention;

FIG. 4 is a diagram showing a time slot allocation for NAK suppressionaccording to the embodiment of the invention;

FIG. 5 is a flow chart showing a method for receiving a data block froma transmitter according to the embodiment of the invention; and

FIG. 6 is a flow chart showing a method for multicasting or broadcastinga data block to a plurality of receivers according to the embodiment ofthe invention.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

A description will now be given with reference to attached figures toillustrate many advantages/features of the present invention, accordingto an illustrative embodiment.

FIG. 1 is a schematic diagram showing a wireless network implementing aTime Division Multiplex (TDM) scheme used to explain an embodiment ofthe invention. As shown in FIG. 1, the wireless communication network100 includes content server 102 having content data for multicast orbroadcast to a multicast group 107. The content data may be for examplea video stream, a video file, an audio file or other data and anycombination thereof. Base station 104 obtains the content from contentserver 102. Base station 104 arranges the content data into a series ofdata blocks and encodes those data blocks according to a rateless codesuch as fountain code, Luby Transform code, process or fixed rate codesuch as Reed-Solomon code process and so on. Each of the data blocks isthen sequentially transmitted, in multicast or broadcast mode, to mobileclient (receiver) devices 107-1 to 107-n of a multicast group.

For each data block, the transmitter of base station 104 transmits aninitial set of transmission data packets of the data block to allreceivers of the client devices 107-1 to 107-n. The initial data packetsare actual content data to be transmitted. Upon receiving the datapackets, each receiver determines if it has received sufficienttransmission packets or symbols to decode the data block. If it has notreceived sufficient packets or symbols, the receiver responds with a NAKmessage to base station 104, so that the transmitter transmitsadditional recovery data packets, such as parity data packets or FECpackets and so on, to the receivers. According to the embodiment of theinvention, if a sufficient number or all packets are successfullyreceived, there is no need to send any response by the receivers.

In the present embodiment of the invention, a TDM scheme is employedwhich divides the available bandwidth in each frame into time slots andallocates these time slots by downlink time slot channel and uplink timeslot channel. The content data is transmitted by downlink time slot tothe receivers of the client devices, and the NAK is transmitted byuplink time slot to the transmitter.

FIG. 2 is a diagram showing a TDM allocation scheme according to theembodiment of the invention. As shown in FIG. 2, the available bandwidthin each frame has been divided into time slots, and these time slots areallocated to a downlink time slot channel (DL in FIG. 2) and an uplinktime slot channel (UL in FIG. 2). It is known to one skilled in the artthat the bandwidth allocated for a downlink channel or an uplink channelis not required to be equal or fixed, and that the downlink bandwidth oruplink bandwidth can be allocated in the base station based on trafficloads. In addition, the specific allocation result is multicast orbroadcasted in the ‘MAP’ field at the beginning of each frame, so thateach receiver is aware of the time slot allocated for it to receive ortransmit data.

In the present embodiment, all receivers in a same multicast group areallocated a same uplink time slot to transmit NAK packets, so only oneuplink time slot is allocated. In order to report NAK messages ofmultiple receivers simultaneously using one time slot, the format offeedback message will be defined as an identical one. In synchronizationwireless network, the identical signal from multiple nodes, such asmultiple receivers, will be regarded as multi-path fading, and the basestation can parse the multiple NAK messages successfully. Therefore, theembodiment of the invention can be used in any of such synchronizationwireless network, such as UMTS, HSUPA, TD-SCDMA, IEEE802.16, LTE orsimilar networks.

FIG. 3 is a diagram showing a NAK message format according to thepresent embodiment. As shown in FIG. 3, the NAK message includes twofields, one being the multicast CID (customer identity) or broadcastCID, and the other being a NAK indicator: a value of ‘0’ in this fieldmeans there is no packet loss, and a value of ‘1’ means there is packetloss. For the multiple receivers of a multicast group, the CID fieldwill be the same, that is, the CID of the multicast group. In addition,according to the embodiment, all receivers having packet loss will sendback a NAK message to the transmitter. For those receivers having nopacket loss, the feedback is not needed. Therefore, the same NAK messagewill be sent back to the transmitter. In addition, it is known to oneskilled in the art that other identical message formats can be usedbased on the embodiment.

FIG. 4 is a diagram showing a time slot allocation for NAK suppressionaccording to the embodiment of the invention. In the sender side, theinitial packets or symbols in block 1 (packet 1 to packet 5) are firstlytransmitted. During the block transmission, there is no need to reportacknowledgement from receivers. When the packet 5 is delivered, anuplink time slot will be assigned to all receivers that belong to thismulticast session to report the reception status. If there is any packetloss during the initial symbols transmission in the data block, forexample, receiver 107-1 has loss for P1/P3/P5, receiver 107-2 has lossfor P3 and receiver 107-3 has loss for P2, a NAK message will be sent bythe receivers. In this example, all receivers of the multicast grouphave packet loss for block 1, so each one will report NAK simultaneouslyin the first uplink feedback time slot, by using an identical messageformat as defined in FIG. 3. Upon receiving the NAK, the transmitterwill realize there is at least one terminal device in the multicastgroup having a problem decoding the original data packets, so it willsend an additional recovery packet or symbol R1 in the downlink timeslot of next frame, then allocate another uplink feedback slot in thesame frame as R1. The additional recovery packet can be at least onedata packet or a group of packets.

The iteration of the above mentioned feedback procedure will be doneuntil all receivers capture enough symbols to recover the original datapackets and no NAK is detected in the uplink channel. As shown in FIG.4, the symbol “⋆” indicates NAK is received from the receivers, and atleast one receiver needs additional recovery packets, and the symbol “∘”indicates no NAK is received, and all receivers could recover theinitial packets successfully. According to the embodiment, the NAKfeedback message indicates packet loss whether it is caused by theinitial symbols or by the recovery symbols (such as P3 or R1 in receiver2). When no NAK is detected in uplink channel for block 1, thetransmission for data of block 1 is over and the procedure for the nextdata block is started.

For example, the following block 2 has a better reception status sinceeach receiver only has one packet loss, so that less feedback time isrequired. The different number of the required feedback report timeslots in this sample illustrates the scalability of the proposedmechanism for feedback compression. The required time slot for feedbackreport only depends on the maximum number of loss packets in the datablock, which has no relation with the receiver number. On the otherhand, the feedback report timeslot is not a fixed value, it will bevariable based on the reception condition among receivers. In badreception condition with dense packet loss (e.g. data block 1), therecovery symbols will be delivered multiple times, while in goodreception condition (e.g. data block 2) with sparse packet loss, only asmall number of recovery data packets is required.

Alternatively, in order to reduce delay of symbol transmission becauseof the insertion of recovery symbols, one method is to adjust the numberof the first recovery packets dynamically based on the statistics of thefeedback report during a given time interval. For example, based on thestatistics, an average number of recovery packets used in several datablocks is 5. Then during a time period under the same situation, thefirst recovery packets in the downlink time slot will include 5additional recovery packets that will be sent to the receivers of themulticast group.

Another method is to set a predetermined condition to terminate thefeedback procedure. For example, the predetermined condition can be themaximum number of recovery symbols for a given block or the maximumallowable time period of transmitting the recovery symbols for a givenblock. If the set threshold value is reached, the feedback procedure ofsending NAK data packets will be terminated and the transmitter willmulticast or broadcast the next data block.

FIG. 5 is a flow chart showing a method for receiving a data block froma transmitter according to the embodiment of the invention. As mentionedabove, the receiving method is used by a plurality of receivers of amulticast group in a synchronization communication network. Thedescription below will address the case of a single receiver—of course,the other receivers will do the same. At step 501, a receiver receivesmulticast (or, according to a variant, broadcast) initial packets from atransmitter of the system, wherein the initial packets can be one ormore data packets. Then, at step 502, the receiver determines whethersufficient initial packets have been received by each of the receivers.If that is not the case, at least one NAK packet is sent by the receiverto the transmitter at step 503. The at least one NAK packet is send inone uplink time slot, and has the same message format as the one used bythe other receivers. At step 504, the additional recovery packet orpackets will be received from the transmitter. After receiving theadditional packets, the receiver will determine if there is still packetloss (step 502), and the step 503 will also be performed repeatedly.Then at step 505, recovering the initial packets is performed by thereceivers. Alternatively, if the predetermined condition is reached asmentioned above, the receivers will terminate the step 503, and performstep 505 directly by the received initial data packets and theadditional packets of the data block.

FIG. 6 is a flow chart showing a method for multicasting or broadcastinga data block to a plurality of receivers according to the embodiment ofthe invention. At step 601, the transmitter multicasts or broadcasts atleast one initial data packet of the data block. The number of theinitial data packets is based on the corresponding coding scheme of thedata block. In addition, an uplink time slot for NAK feedback will beallocated to the plurality of receivers of the multicast groupsimultaneously in the MAP field of the frame. Then the transmitterdetermines whether at least one NAK feedback packets is received duringthe allocated uplink time slot at step 602. The at least one NAK has thesame message format for all receivers, and as such can be considered asone message. No congestion will be caused. Then at step 603, at leastone additional recovery data packet will be multicast or broadcasted bythe transmitter when the NAK packet is received. If no NAK packet isreceived or a predetermined condition occurs, the transmitter willterminate sending packets of the data block and move to next data blockat step 504.

Although a synchronization network is used to explain the presentembodiment, one skilled in the art knows that the method of sending andreceiving data blocks of the embodiment can be used only if the singletime slot allocated to a group of receivers is a time slot of asynchronization uplink channel despite the network is synchronized ornot. In addition, although the data block in the embodiment is recitedto be sent by multicast mode or broadcast mode, one skilled in the artknows that the method can be used only if a single time slot isallocated to a group of receivers, and despite the style of sending thedata block.

The foregoing merely illustrates the embodiment of the invention and itwill thus be appreciated that those skilled in the art will be able todevise numerous alternative arrangements which, although not explicitlydescribed herein, embody the principles of the invention and are withinits spirit and scope.

The invention claimed is:
 1. A method for receiving a data blockcomprising at least one data packet from a transmitter, used in areceiver part of a multicast group of receivers in a communicationnetwork, including: a. receiving said at least one data packet of thedata block; b. if insufficient data packets have been received in orderto decode said data block due to packet loss, sending anegative-acknowledgment (NAK) message during a same time slot allocatedto all receivers of the multicast group and wherein said NAK message isidentical for all receivers of the multicast group; c. receiving atleast one recovery data packet from said transmitter; and d. repeatingsteps b and c until a predetermined condition is met.
 2. The methodaccording to claim 1, wherein the same time slot is a time slot of asynchronization uplink channel.
 3. The method according to claim 1,further including the step of sending is performed if there is stillpacket loss so as to have a problem of decoding the data block at the atleast the receiver after receiving the at least one recovery datapacket.
 4. The method according to claim 3, wherein data packets takeninto consideration for sending a NAK message include said at least onedata packet and at least one recovery data packet.
 5. The methodaccording to claim 1, wherein the predetermined condition is the maximumnumber of recovery symbols for a given data block or the maximumallowable time period of transmitting the recovery symbols for a givenblock.
 6. A receiver for implementing the method for receiving a datablock according to claim
 1. 7. A method for sending a data blockcomprising at least one data packet to a multicast group of receivers,used in a transmitter of a communication network, including: a. sendingsaid at least one data packet of the data block; b. providing a sametime slot for all receivers of the multicast group to send a NAKmessage, wherein the NAK message is the same for all receivers from themulticast group; c. if a NAK message is received: d. sending at leastone recovery data packet to the receivers of the muiticast group; e.providing a further same time slot for receivers of the multicast groupto send a further NAK message; and f. repeating steps c to e until apredetermined condition is met.
 8. The method according to claim 7,wherein the uplink time slot is a time slot of a synchronization uplinkchannel.
 9. The method according to claim 7, wherein the further NAKmessage indicates packet loss of said at least one data packets or saidat least one recovery packets.
 10. The method according to claim 7,wherein the predetermined condition is a number of the further sendingsteps.
 11. A transmitter for implementing the method for transmitting adata block according to claim 7.